The shaker head apparatus is necessarily massive and heavy. Shakers are typically mounted on trunnions so that the head may be directed horizontally or vertically and thus the shaker head is carried for angular movement relative to the slip plate. The slip plate is supported on a bearing table atop a mass which is necessarily quite heavy and not ordinarily considered movable. In making a test set-up, the slip plate is fastened down carefully to the bearing table so that movement only in desired axes occurs. The driver bar coupled to the shaker head is jockeyed into place on the slip plate edge margin and the split sleeve pins inserted. The operation has typically required relative movement of the slip plate and shaker head, followed by fastening down of the slip plate. Any adjustment in the test set-up requires unbolting the slip plate, or movement of the shaker head. Because driver bars typically extend both over, and under, the slip plate edge margin, the shaker head cannot be simply tipped up out of the way. In U.S. Pat. No. 3,933,033, a solution to this problem was disclosed in the form of a cantilever driver bar. In certain applications, particularly small set-ups, the non center line to center line nature of the relationship of the driver bar flange and the slip plate is disadvantageous and thus there is a need to provide a driver bar which is convenient to use, like that of U.S. Pat. No. 3,933,033, but which drives the slip plate in opposed relation on a center line to center line basis in a common plane, without unwanted pitch moments.